The present invention relates to hot runner edge gating nozzle for molding thin flat articles, particularly smart cards.
Flat parts of constant cross section thickness are typically gated at one end so that the molten plastic material, such as a plastic resin, flows the longest path to fill the part. In this way, molded in stresses which cause warpage are avoided. Such parts preferably are molded using an edge gate rather than a pin gate into one of the larger surfaces, because injecting the plastic material perpendicularly to the flow direction for filling can cause part blemishes, such as jetting, and warpage. Injecting the plastic material aligned with the flow direction for filling minimizes these problems.
Smart cards are wallet size plastic cards containing an embedded computer chip. The chip is an integrated circuit that can be preprogrammed to interact with sensors and readers that the card may come into contact with. Injection molding smart cards is becoming the preferred method of manufacture. The paper "Why Automation for Chip Cards", by Truckenbrod summarizes the current state of the smart card art. When using an injection molding technique, it is important to design the mold cavity gates so that flat warp free cards are molded without any gate vestige that may cause injury when the cards are handled.
Published European Patent Application No. 0 800 908 to Herbst shows an edge gating technique for molding articles such as smart cards. FIGS. 6 and 7 in this document show a sleeve that is advanced to sever the gate. If this sleeve is cylindrical, then the severed edge of the part will not be linear but rather circular. This technique is not well suited for making rectangular style cards.
Published European Patent Application 0 800 907 to Manner shows a conventional hot runner valve gate having a melt passage cut into the valve stem that feeds plastic resin transversely into the side of a mold cavity--in effect an edge gate. Again, the valve stem is cylindrical and will not produce a flat vestige free surface on the flat edge of a rectangular part.
U.S. Pat. No. 5,460,509 to Sawafuji shows a cold runner edge gating system with opposed knives that sever the frozen runner. U.S. Pat. No. 2,890,488 to Gemberling shows a movable hot runner nozzle that severs the gate after filling the cavity; however, pin gating into a flat surface is only shown.
Co-pending U.S. patent application No. 09/036,132 now U.S. Pat. No. 6,161,899 shows a slide gate approach for closing a hot runner pin gate.
None of these prior art documents illustrates how to hot runner edge gate a rectangular shaped article along a flat side to make a vestige free gate mark.